This invention relates to carbon monoxide warning systems, and in particular, to systems for alerting an occupant of an excessive level of carbon monoxide gas.
As a result of the increased concern over the dangers of carbon monoxide, many types of carbon monoxide detectors are currently available for sale to the public. These devices typically include a detection circuit that triggers an audible alarm to alert occupants of a harmful level of carbon monoxide gas. To provide further protection to the occupant, improvements have been made to disable the operation of gas-fired heaters, which may potentially be the source of the carbon monoxide gas. Such a device is disclosed in U.S. Pat. No. 5,793,296 issued to Lewkowicz, or in U.S. Pat. No. 5,838,243 issued to Gallo. However, upon detecting the presence of carbon monoxide gas, these devices either disable the operation of a thermostat connected to a heating system, or disable the flow of natural gas to a furnace or boiler. Installing such devices in primarily unoccupied vacation homes could potentially cause freezing damage to water pipes, resulting from the disabling of heating systems. Thus, there is still a need for a device that will both alert occupants of a harmful level of carbon monoxide gas and maintain the operation of a gas-fired heating system at a reduced level, to prevent potential freezing damage and reduce the potential for further carbon monoxide production.
There is provided, in accordance with one aspect of the invention, a digital thermostat comprising an LCD display or an audible alarm, and input means for receiving at least one signal from at least one carbon monoxide detector external to the thermostat. The thermostat is configured to trigger the audible alarm or flash a warning on the LCD display when receiving at least one signal from at least one carbon monoxide detector indicating the presence of a predetermined level of carbon monoxide gas. The thermostat is also configured to lower the set point temperature to approximately 50xc2x0 F. to prevent potential freezing damage to water pipes and to reduce the potential for further carbon monoxide production. The minimal set point temperature of 50xc2x0 F. could also prompt hearing-impaired occupants to view an LCD display, which would alert them of the presence of carbon monoxide gas with a flashing warning. The 50xc2x0 F. set point, audible alarm, and flashing warning would remain in effect until the thermostat is manually reset.
In accordance with another aspect of the invention, the digital thermostat comprises a plurality of sensing means for sensing input signals received from at least one carbon monoxide detector external to the thermostat. One such sensing means comprises a filter circuit that monitors the waveform of the current through the thermostat""s 24 VAC xe2x80x9cheat loadxe2x80x9d terminals, which connect to a furnace control that incorporates a carbon monoxide detector. The furnace control may be configured to switch or chop the 24 VAC signal to the thermostat when the carbon monoxide detector indicates the presence of a predetermined level of carbon monoxide gas. The thermostat""s filter circuit detects any high frequency fluctuations in the 24 VAC waveform generated by the furnace control and isolates the fluctuations as a signal, which may communicate the carbon monoxide level sensed by the furnace control""s carbon monoxide detector. Another sensing means comprises a microprocessor in the thermostat that senses the presence of current through a second set of input terminals, which may be connected directly to a second external carbon monoxide detector.
It is thus an object of the invention to provide a thermostat that can receive signals from an external carbon monoxide detector indicating a harmful level of carbon monoxide gas, alert an occupant of the carbon monoxide, and reduce the operation of a gas-fired heating system which may potentially produce such carbon monoxide gas, without disabling the heating system.
It is a further object of the invention to provide a thermostat that comprises signal input monitoring means for a plurality of carbon monoxide detectors external to the thermostat, and that is configured to trigger an audible alarm and or flashing warning on the LCD display when receiving at least one signal from said detectors indicating a harmful level of carbon monoxide gas.